Escapement



Nov. 10, 1970 M. R. PERRY 3,538,705

ESCAPEMENT I Filed Nov. 7, 1968 E s Sheets-Sheet 1 UNIDIRECTIONAL DRIVE I l R v fl 248 PALLET o DISPLACEMENT 2 3 E; 0 PALLET DISPLACEMENT E I vs 2 o ESCAPE WHEEL ROTATION BEAT 0 POSlTiON 0 LEGEND! I E 1 STRAIGHT LINE a cm IMPULSE SURFACE 3 THEORETICAL CONVENTIONAL o ESCAPEMENT HAVING LOCK v AND |DROP v 5 LOCK 60 I l l 1 J 1- 1 E I INVENTOR. (3.5 v MALCOLM R. PERRY BY zww ATTORNEYS I ESCAPEMENT Filed Nov. 7, 1968 3 Sheets-Sheet 2 H020 HG2b 12 |2- K IN V EN TOR. MALCOLM R. PERRY ATTORNEYS Nov. 10, 1970 M. R. PERRY v- 3,538,705

, ESdAPEMENT Filed Nov. 7 1968 3' Sheets-Sheet 3 INVENTOR MALCOLM R. PERRY ATTORNEYS United States Patent Oflice Patented Nov. 10, 1970 3,538,705 ESCAPEMENT Malcolm R. Perry, Lancaster, Pa., assignor to Hamilton Watch Company, a corporation of Pennsylvania Filed Nov. 7, 1968, Ser. No. 774,123 Int. Cl. G04b /00; F16h 27/00 U.S. Cl. 58-116 16 Claims ABSTRACT OF THE DISCLOSURE The present escapement includes a pallet and escape wheel manufactured to accept broad tolerances with the pallet and escape Wheel having flat configurations. The locking and impulse surfaces on the pallet, as well as on the escape wheel teeth, are formed with corner radii. The present escapement provides for an effective deep lock. of about 3, a drop of about 4, neutral draw, and high impulse energy near the zero beat position, to improve self-starting characteristics, minimize input torque motions sensitivity and substantially eliminate the possibility of setting or locking on an impulse surface.

The present invention relates to an escapement for clockwork and watch mechanisms and particularly relates to an improved escapement formed to accept broad manufacturing tolerances and having corner radii on the cooperating surfaces of the escapement as well as other features.

Present escapements for watches and clockwork mechanisms of the type having a pallet mounted for oscillatory movement and an escape wheel mounted for stepping rotary movement in one direction under the control of the pallet, are normally high precision devices requiring close tolerances. For example, the corners on the pallet stones and the cooperating escape wheel teeth are normally designed for extremely sharp corners which require tolerances on the order of .0002 to .0005. Much time, effort, and expense has gone into the manufacture of such closely toleranced precision escapement and the usual method for fabricating these conventional escapements is to stamp over-sized parts and then bend and shave, machine (wheel cutter or miller) and form the parts to the designated close tolerances. These extremely close tolerances are impossible to maintain, merely by stamping and shaving the parts, and these additional forming, bending, and machining operations are necessary to conform the impulse and locking surfaces of the pallet stones and escape wheel teeth to the closely toleranced precision design. These additional operations are, of course, time consuming and increase the overall cost of the complete timekeeping mechanism,

Apart from the foregoing described difficulties in the manufacture of watch and clockwork mechanisms, conventional escapements are somewhat ineflicient in operation in many respects. For example, in most escapement designs the force of an escape wheel tooth on the locking surface of a pallet stone normally draws the stone deeper into the escape wheel. This usually requires that the escape wheel as well as, in some instances, the watch or clockwork train geared to the escape wheel, first back up before the escape wheel can subsequently impulse the pallet. This condition is deleterious to self-starting and also dissipates energy from the balance wheel as the energy to back up the escapement and the gear train where applicable must come from the balance wheel momentum and/or the hairspring deflection force. This, in turn, makes the escapement input torque sensitive.

Additionally, certain escapements require high impulse energy to initiate timekeeping. Where the escapement is locked, the initial impulse energy may be insufficient with the result that the escapement remains in a locked condition. This is a particular disadvantage in time totalizing meters wherein the timekeeping function is periodic and self-starting is essential. Moreover, in many closely toleranced watch or clockwork escapements, there is always the possibility of the escape wheel teeth setting on an impulse surface and locking the escapement. These disadvantages and inefficiencies in the manufacture and performance of conventional escapements, are substantially eliminated or minimized by the escapement of the present invention.

The present escapement includes a pallet and an escape wheel which are formed to accept broad or liberal tolerances and yet satisfactorily and reliably perform their intended timekeeping function. Unique functional features discussed below, such as, for example, neutral draw, a deep lock, minimum input torque sensitivity, impulse areas in shapes calculated to provide high impulse near the zero beat position, etc., are provided the present escapement making it possible to accept such liberal manufacturing tolerances, whereby the escapement may be manufactured for less cost, adjustment of its parts, jobbing, etc, as compared with conventional escapements. Particularly, it has been found possible to form the pallet and escape wheel of the present invention solely by a stamping operation without additional fabricating operations such as bending, shaving, forming, machining or the like, and to form such parts completely flat. Thus the parts of the present invention can be readily manufactured. Concomitantly, the completed and assembled escapement can function as a high precision timekeeping mechanism within a predetermined accuracy.

One unique aspect of the present escapement provides for the formation of corner radii between adjoining locking and impulse surfaces on the pallet stones and escape wheel teeth. By designing the escapement with such corner radii, liberal tolerances can be assigned making it possible to permit the formation of the pallet and escape wheel solely by a stamping operation or other manufacturing techniques such as injection molding, aluminum die casting, and the like, wherein the usual extremely close tolerances required in conventional escapements cannot be obtained. The provision of corner radii also permits the formation of a flat pallet and escape wheel.

Another unique aspect of the present escapement provides for neutral draw. By shaping the locking and impulse surfaces of the pallet stones and the escape wheel teeth in a unique manner and within the liberal predetermined tolerances, all in accordane with the present invention, the usual backing-up action of the escape wheel and often the gear train unlocking the pallet in conventional escapements is eliminated. The energy dissipation which normally occurs when the pallet is unocked is thus completely eliminated. Apart from this, the elimination of draw facilitates self-starting, provides for less input torque sensitivity and permits a deeper lock, i.e., the escapement is less lock sensitive.

A further feature hereof provides for improvement'of the self-starting characteristics of the timepiece as well as minimizing the possibility of setting or locking on an impulse surface. To accomplish this, the balance wheel hairspring is set to provide no force at the zero beat position and the pallet and balance are formed to provide a high balance wheel to pallet angular displacement ratio. With this arrangement, the force of the hairspring in returning the balance to the zero beat position is significantly greater than in conventional escapements thereby facilitating unlocking of the pallet. Moreover, the possibility of setting on an impulse face is substantially decreased. To this end, the impulse and locking surfaces of the pallet stones and escape wheel teeth are shaped to provide maximum impulse energy to the balance near the zero beat position. The ratio of angular displacement of the pallet and the escape wheel when the pallet passes through the zero beat position is about 1:1 whereas the escape wheel rotates about 2 for every degree of rotation of the pallet during the latter half of the impulse period. The higher mechanical advantage of the escape Wheel near the zero beat position of the pallet thus increases the self-starting characteristics of the present escapement and avoids setting on impulse surfaces.

Accordingly, it is a primary object of the present invention to provide an improved escapement for watch and clock mechanisms.

It is another object of the present invention to provide an improved escapement having parts which can be readily and easily manufactured at low cost.

It is still another object of the present invention to provide an improved escapement formed to accept broad tolerances and affording accurate and precision timekeeping.

It is still a further object of the present invention to provide an escapement having neutral draw wherein the pallet is unlocked without backing up the escape wheel and drive train.

It is a still further object of the present invention to provide an escapement having improved self-starting characteristics and minimum torque sensitivity.

It is a related object of the present invention to provide an improved escapement wherein the parts are formed to accept broad tolerances, formed flat and thereby may be manufactured, for example, solely by stamping operations.

It is a further related object of the present invention to provide an improved escapement having a high balance Wheel to pallet angular displacement ratio and wherein the cooperating surfaces of the pallet and escape wheel are formed to provide high impulse energy near the zero beat position.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, drawings and claims.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an escapement constructed in accordance with the present invention;

FIGS. 2a-2d are reduced plan views of the escapement illustrating a complete cycle of operation;

FIGS. 3 and 4 are fragmentary enlarged plan views respectively illustrating the pallet arms in locked position with the teeth of the index wheel;

FIG. 5 is a graph illustrating pallet displacement as a function of scape wheel rotation;

FIG. 6 is a side elevational view of the escapement illustrated in FIG. 1;

FIGS. 7-8 are fragmentary enlarged plan views of the pallet arms and index wheel teeth; and

FIGS. 9-10 are enlarged fragmentary plan views of another form of pallet arm surfaces.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGS. 1 and 6, there is shown an escapement comprising a pallet and an escape wheel 10 and 12, respectively, which form an integral part of a timepiece or watch mchanism. Pallet 10 is mounted on a pallet staff 14 pivotally carried by base plates, one of which is shown at 15 (FIG. 6), mounted in a timekeeping mechanism and escape wheel 12 is mounted on a staff 13 pivotally car- 4 movement of pallet 10 about staff 14. Index wheel 12 is geared to the gear train of the timepiece or watch in the usual manner.

One end of pallet 10 is bifurcated to form a pallet fork having a recess 22 between its fingers 24 in the usual fashion. A balance assembly generally indicated at 26 cooperates with the pallet 10 to oscillate the latter about axis 14 and comprises a balance staif 28 carrying an indexing roller 30 mounting a depending roller pin 32. Balance staff 28 is suitably drivingly connected in the usual manner to a balance wheel and hairspring assembly, not shown, whereby roller pin 32 oscillates about the axis of staff 28. A guard roller 34 having a recess 36 formed in the periphery thereof is also carried by staff 28 and cooperates with a guard pin 38 carried on pallet 10 to prevent overbanking. It will thus be seen that roller pin 32 releasably engages within recess 22 to oscillate pallet 10 about pivot 14, the oscillatory excursion in either direction being arrested by the engagement of pallet 10 against respective banking pins 10.

Referring now to FIGS. 2a-2d, the movement will now be described. In FIG. 2a, the escape wheel and pallet are illustrated in the Zero beat position with no torque applied to escape wheel 12. It will be noted that impulse surface 201 of an escape wheel tooth 20 engages the impulse surface 18I of pallet arm 18. When torque is applied to escape wheel 12, as by winding he mainspring of the timepiece or watch or by operation ofa machine when the escapement is employed in a time totalizing meter, the impulse surface 201 of the engaged tooth 20 cooperates with impulse surface 181 on pallet arm 18 to drive pallet 10 in a clockwise direction against a banking pin 40 as illustrated in FIG. 2b. The impulse provided pallet 10 by index wheel 12 drives and pivots roller pin 32 out of engagement in recess 22 in a counterclockwise direction against the bias of the hairspring, not shown. It will be noted that, when pallet 10 is impulsed against banking pin 40, the impulse tooth 20 rotates beyond and clears pallet arm 18 and, with continued torque applied to index wheel 12 by the mainspring or other energy source of the timepiece as indicated at 10, the index wheel 12 rotates until the locking surface 20L of an index wheel tooth 20 engages the locking surface 16L of pallet arm 16 whereby further rotation of index wheel 12 is restrained. Upon completion of the counterclockwise oscillatory excursion of roller pin 32 and with pallet 10 remaining in the banked position, the hairspring, not shown, drives roller pin 32 in the opposite clockwise direction to engage in recess 22 and pivot pallet 10 in a counterclockwise direction as illustrated in FIG. 2c. In pivoting pallet 10 from the banked position of FIG. 2b through its center position illustrated in FIG. 20, the locking surface 16L is withdrawn from engagement with the locking surface 20L on the index wheel tooth 20 such that the impulse surface 201 on tooth 20 engages the impulse surface 161 of pallet arm 16. The continued torque applied to index wheel 12 as well as the continued oscillatory clockwise excursion of roller pin 32 pivots pallet 10 to the opposite banked position illustrated in FIG. 2d. Balance assembly 26 is also impulsed by pallet 10 such that roller pin 32 continues on its clockwise oscillatory excursion against the bias of the hairspring, not shown. It will be noted that the pivoting action of pallet 10 past its center position perm-its the impulse tooth 20 to advance beyond and clear pallet arm 16 with rotational movement of index wheel 12 then being restrained (FIG. 2d) by the engagement of the locking surface 20L of a next index wheel tooth 20 against the locking surface 18L of pallet arm 18. Upon completion of the clockwise oscillatory excursion of roller table 39, roller pin 32 returns on its counterclockwise excursion to engage in recess 22 and pivot pallet 10 clockwise. The impulse surface 201 of tooth 20 thus engages the impulse surface 181 of pallet arm 18 to impulse pallet 10 and balance assembly 26 thereby displacing the pallet and the balance assembly to the position illustrated in FIG. 2b. This cyclic movement is repeated for so long as torque is applied to escape wheel 12.

It is a significant feature of the present invention that the pallet and escape wheel and 12, respectively, are formed to accept broader tolerances in the manufacture thereof than heretofore accomplished and that the present escapement has excellent performance and reliability characteristics contrary to that which might normally be expected with such broader tolerances. For example, conventional clock and timer escapements are tolerated at .0002 to .0005. This conventional design criteria therefore requires precision manufacture of the parts forming the escapement. To my knowledge, all prior escapements are high precision mechanisms designed for sharp corners on the cooperating pallet arms and index wheel teeth and have close tolerances on the order of those mentioned above. The forming and machining operations such as the bending, cutting and/or milling operations nec essary to achieve such close tolerances are, of course, time consuming and expensive. Contrary to this conventional design criteria, the present escapement is formed to accept broader tolerances on the order of .005 to .0020. This provides a less tolerance sensitive escapement than is conventional and one which can be readily and easily manufactured at less cost and adjustment as well as other features to be described.

It is a particular feature of the present invention that the pallet and escape wheel are formed fiat. That is, the teeth on escape wheel 12 and the pallet arms 16 and 18 including their respective locking and impulse surfaces lie wholly within the corresponding planes of index wheel 12 and pallet 10. By forming the pallet and escape wheel flat and to the specified liberal tolerances, it has been found possible to completely form the pallet and index wheel without the bending, forming, milling, shaving, or performing like operations characteristic of the manufacture of prior escapements. Pallet 10 and index wheel 12 are preferably stamped from sheet metal, for example, stainless steel, and assembled in operative relation one to the other without additional manufacture. It will be noted that the formation of the pallet and index wheel are complementary one to the other and tha a flat pallet formed in accordance with the above-noted criteria would be ineffective if employed with an index wheel formed employing usual design criteria. Likewise, an index Wheel formed in accordance with the present invention would also be ineffective if employed with a pallet formed in a conventional manner. It will be appreciated, of course, that the pallet and escape wheel can be formed flat by other manufacturing operations. For example, the parts of the present escapement may be manufactured to the required semi-precision by injection molding, aluminum die casting, powder metallurgy or the like. It will also be noted that guard pin 38 is preferably staked to pallet 10 although it could be formed as an integral part thereof when employing any of the manufacturing processes noted above.

The present escapement provides for corner radii on the pallet arms or stones and escape wheel teeth. Specifically, as seen in FIGS. 3 and 4, the corners between the locking and impulse surfaces 16L, 18L and 1 61, 18L respectively, and between the impulse surfaces 16I, 181 and leading edges 16E, 18E, respectively, have radii by design in contradistinction to the normally provided sharp or pointed corners on conventional escapements of this type. By providing for corner radii, the pallet and escape wheel may be manufactured flat and by a sheet metal stamping operation. Additionally, punch and die life are increased. The pallet stone and index wheel teeth are shaped to compensate for corner radii to provide optimum performance characteristics such as improved self-starting characteristics, neutral draw, minimum input torque sensitivity, high impulse energy near the zero beat position, and others discussed hereinafter.

Two types of pallet arm surfaces formed in accordance with the present invention are herein illustrated. In FIGS. 7 and 8, there is shown straight line impulse surfaces 161 and 18I and in FIGS. 9-10,,there is illustrated cam type impulse scrfaces 161C and 181C. Both straight and cam impulse surfaces are designed to provide greater energy during the initial impulse period and less energy during the latter part of the period to provide less input torque motion sensitivity and decrease the possibility of setting on impulse surfaces as hereinafter more fully described. The employment of one or the other depends on the degree of performance (accuracy, self-starting) that is desired and it will be noted that the cam impulse surfaces are defined by combined arcuate and straight edges.

In a preferred embodiment hereof (FIGS. 78), the index Wheel 12 has 12 equally-spaced teeth, radii of .1825 and .1888 inch at points 1 and 2, respectively, a tooth width of .0195 inch at 3, and corner radii of .0020 inch. The locking surfaces 20L of the teeth lie on radii of the wheel 12. The wheel is preferably formed of stainless steel with the locking and impulse surfaces having a number 16 polish. The center to center distance of the balance to pallet staffs and the pallet staff to the index wheel staff is .3500 and .2300 inch, respectively, with lines extending from the balance and index wheel axes through the pivot axis of the pallet forming a right angle.

The following tables provide dimensions in X and Y directions as seen in FIG. 1 of the numbered positions of the pallet arms 16 and 18 (FIGS. 710) from a reference coincident with the axis of pallet 10, the reference point having an X and Y value of 2.000.

STRAIGHT LINE SURFACES (FIGS. 7-8) Reference point X Y The corner radii on the pallet arms are formed at .0020 inch. The radii in FIGS. 9 and 10 of the curved surface portions having centers at reference points 23 and 31 are .0302 and .0360 inch, respectively.

The present escapement is characterized by improved self-starting characteristics. To this end, a high balancepallet angular displacement ratio is employed. Since the hairspring can thus store more energy for the same pallet displacement than would otherwise be the case, unlocking of the escapement is greatly facilitated. In a preferred form hereof, the ratio of the total displacement of the balance wheel while engaged with the pallet to the total displacement of the pallet is about 4.2. With the hairspring on the balance wheel set to provide no force at the zero beat position, the balance wheel will zero beat itself after power has been removed. In this manner, one or the other of the impulse surfaces 161 or 181 is always aligned with an escape wheel tooth impulse surface 201 thus avoiding alignment of the pallet and escape wheel in a locked condition. Moreover, pallet stones 16 and 18 and escape wheel teeth 20 are shaped such that the force applied by the escape wheel tooth is very nearly normal to the pallet impulse surfaces at the Zero beat position of the pallet thereby further improving the self-starting characteristics of the present escapement.

To preclude the possibility of setting on an impulse surface when a high balance-pallet displacement angular ratio is employed, most of the impulse energy to the balance is provided near the zero beat position. As illustrated by the graph depicted in FIG. 5, wherein the solid and dashed lines represent the cam impulse and straight line surfaces, respectively, less than one-third of the pallet displacement angle remains while one-half of the escape wheel rotation remains. In other words, a high impulse is provided the pallet near the zero beat position with the pallet being displaced about a full degree for each degree of rotation of the escape wheel. During the last half of the impulse period, the escape wheel rotates about 2 to displace the pallet one degree. This high impulse energy near the zero beat position improves the self-starting characteristics hereof by providing a sulfcient initial impulse to the pallet and hence to the balance assembly when the escapement is in the rest position to insure unlocking of theescapement and avoid the possibility of setting on an impulse surface.

Additionally, by providing an escapement having the broad tolerances and the corner radii noted previously, draw, that is, the force of an escape wheel tooth on the pallet stone locking surface which would normally pull the stone deeper into the escape wheel or conversely the force conventionally required to back up a gear train in order to unlock the pallet, is eliminated. Thus, in selfstarting, the timepiece need not overcome or back up the gear train or remove energy from the balance wheel which would otherwise make the escapement input torque sensitive. The elimination of draw also provides for a deeper lock. While conventional escapements have a 1 lock, the effective lock angle of the present escapement is 3". To be locked, the pallet must be displaced from zero to 3 or more.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. An escapement for a timekeeping mechanism comprising a pallet mounted for oscillatory movement and having a pair of pallet arms, each of said arms having integral impulse and locking surfaces, means for oscillating said pallet, an escape wheel carrying a plurality of teeth, each of said teeth having impulse and locking surfaces cooperatively engageable with corresponding surfaces carried by said pallet arms, means for imparting a torque to said escape wheel, the impulse and locking surfaces of each of the pallet arms and escape wheel teeth being angularly related one to the other with a corner radius therebetween, said corresponding surfaces cooperating to provide unidirectional rotary motion of said escape wheel in response to oscillatory movement of said pallet.

2. An escapement according to claim 1 wherein at least a major portion of said pallet including the pallet arms and the impulse and locking surfaces carried thereby lie in a single common plane.

3. An escapement according to claim 1 wherein at least a major portion of said escape wheel including said teeth and the impulse and locking surfaces carried thereby lie in a single common plane.

4. An escapement according to claim 1 wherein at least the major portions of said pallet and said escape Wheel including their respective pallet arms and teeth and the impulse and locking surfaces carried thereby each lie in respective common planes.

5. -An escapement according to claim 1 wherein at least a major portion of the escape wheel including the escape Wheel teeth lie in a single common plane, the impulse and locking surfaces of each of said teeth, extending in next adjacent angular relation one to the other, each tooth having a third surface extending in said plane at an angle and next adjacent to the associated impulse surface, said third and impulse surfaces having a radius therebetween.

6. An escapement according to claim 1 wherein said locking and impulse surfaces on said pallet and said escape wheel are formed to provide neutral draw.

7. An escapement according to claim 1 wherein said locking and impulse surfaces on said pallet and said escape wheel are formed to provide maximum impulse energy at substantially the zero beat position of the pallet.

8. An escapement according to claim 1 wherein said pallet and escape wheel are formed to accept tolerances on the order of .0005 to .0020 inch.

9. An escapement for a timekeeping mechanism comprising a pallet mounted for oscillatory movement and having a pair of pallet arms, means for oscillating said pallet, an escape wheel carrying a plurality of teeth cooperatively engageable with said pallet arms, and means for imparting a torque to said escape wheel, the cooperating surfaces of the pallet arms and escape wheel teeth providing unidirectional rotary motion to said escape Wheel in response tooscillatory movement of said pallet, said pallet including said arms and said escape wheel including said teeth being formed flat and lying in coplanar relation one with the other. I

10. An escapement according to claim 9 wherein said pallet arms and said escape wheel teeth have locking and impulse surfaces formed to provide neutral draw in operational usage.

11. An escapement according to claim 9 wherein said pallet arms and escape Wheel teeth having locking and impulse surfaces formed to provide maximum impulse energy at substantially the zero beat position of the pallet.

12. An escapement according to claim 9 wherein said pallet and escape wheel are formed to accept tolerances on the order of .0005 to .0020 inch.

13. An escapement according to claim 9 wherein the cooperating surfaces of said pallet arms and said escape wheel teeth each include angularly related surfaces having a corner radius therebetween.

14. An escapement for a timekeeping mechanism comprising a pallet mounted for oscillatory movement and having a pair of pallet arms, means for oscillating said pallet, an escape wheel carrying a plurality of teeth cooperatively engageable with said pallet arms, means for imparting a torque to said escape wheel, the cooperating surfaces of the pallet arms and escape wheel teeth each including angularly related surfaces having a corner radius therebetween and providing uni-directional rotary motion of said escape wheel in response to oscillatory movement of said pallet, at least major portions of said pallet and escape wheel including their respective pallet arms and teeth lying in co-planar relation one with the other.

15. An escapement for a timekeeping mechanism comprising a pallet mounted for oscillatory movement and having a pair of pallet arms, means for oscillating said pallet, an escape wheel carrying a plurality of teeth cooperatively engageable with said pallet arms, means for imparting a torque to said escape wheel, the cooperating surfaces of the pallet arms and escape wheel teeth each including angularly related surfaces having a corner radius therebetween and providing uni-directional rotary motion of said escape wheel in response to oscillatory movement of said pallet, at least a major portion of the pallet including the pallet arms lying in a single common plane, the angularly related surfaces of said pallet arms comprising impulse and locking surfaces extending in next adjacent angular relation one to the other, each pallet arm having a third surface extending in said plane at an angle and next adjacent to the associated impulse surface, said third surface and impulse surfaces having a radius therebetween.

16. An escapement for a timekeeping mechanism comprising a pallet mounted for oscillatory movement and having a pair of pallet arms, means for oscillating said pallet, an escape wheel carrying a plurality of teeth cooperatively engageable with said pallet arms, means for imparting a torque to said escape wheel, the cooperating surfaces of the pallet arms and escape wheel teeth each including angularly related surfaces having a corner radius therebetween and permitting uni-directional rotary motion of said escape wheel in response to oscillatory movement of said pallet, both said pallet and said escape wheel 10 lying in a single common plane, each of said pallet arms and said escape wheel teeth having adjacent locking, impulse and third surfaces extending in angular relation one to the other, said arms and said teeth having corner radii disposed between said adjacent surfaces.

References Cited UNITED STATES PATENTS 1,979,028 10/1934 Ewart 235-91 X 3,017,742 1/1962 Reinhardt 58-16 3,425,212 2/1969 Verde 58116 FOREIGN PATENTS 1,473,355 2/1967 France.

RICHARD B. WILKINSON, Primary Examiner S. A. WAL, Assistant Examiner U.'S. Cl. X.R.

UNITED STATES PATENT CERTIFICATE OF CORRECTION,

Patent No. 3,538,705 Dated No b 10, 1910 Inventor(s) MALCOLM RRY It is certified that error appears in the above-identified patent and that; said Letters Patent are hereby corrected as shown. below:

Column 2, line 53, "unocked" should read unlocked Column line 50, "scape" should read escape line 63, "mchanism" should read mechanism line 75, "rsponse" should read response .Column 4, line 27, "he" should read the Column 5, line 23, ".005" should reac .0005 line 43, "tha" should read that Column 6, line 5,

"scrfaces" should read surfaces Column 7, line 25, "suffcient" ShOL read sufficient Signed and sealed this 27th deg of April l 973 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SC 0 l R, JR Atte sting Officer Commissioner 0 Patents 

